U.S. patent number 4,866,350 [Application Number 07/177,161] was granted by the patent office on 1989-09-12 for fluorescent lamp system.
This patent grant is currently assigned to Usi Lighting, Inc.. Invention is credited to Richard C. Counts.
United States Patent |
4,866,350 |
Counts |
September 12, 1989 |
Fluorescent lamp system
Abstract
Power is provided to a fluorescent lamp through a single
integrated circuit (IC) chip. The IC chip contains control logic
and power switches. The control logic operates the switches at a
frequency which is optimum for the fluorescent lamp. The control
logic includes circuits for thermal shut down, load status
detection and voltage compensation.
Inventors: |
Counts; Richard C. (Dallas,
TX) |
Assignee: |
Usi Lighting, Inc. (San
Leandro, CA)
|
Family
ID: |
22647443 |
Appl.
No.: |
07/177,161 |
Filed: |
April 4, 1988 |
Current U.S.
Class: |
315/209R;
315/226; 315/307; 315/309 |
Current CPC
Class: |
H05B
41/2981 (20130101) |
Current International
Class: |
H05B
41/298 (20060101); H05B 41/28 (20060101); H04B
041/36 () |
Field of
Search: |
;315/307,309,29R,29T,226,DIG.2,DIG.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mis; David
Attorney, Agent or Firm: Schatzel; Thomas E.
Claims
I claim:
1. A fluorescent lamp system comprising:
a power source;
a first fluorescent lamp; and
an integrated circuit chip connected intermediate the power source
and the lamp, the chip containing switching means connected to the
power source and the lamp, for delivering power to the lamp, and
control means connected to said switching means for operating said
switching means at a frequency which allows the lamp to operate at
optimum efficiency.
2. The system of claim 1 further comprising,
a current limiting circuit connected intermediate the lamp and the
IC chip.
3. The system of claim 1 further comprising,
a second fluorescent lamp connected to said switching means of the
IC chip and wherein, said control means operates said switching
means to alternately supply power to the first and second lamps at
said frequency.
4. The system of claim 1 wherein,
the IC chip further comprises a rectifier connected intermediate
the power source and said switching means.
5. A fluorescent lamp system comprising:
a power source;
a first fluorescent lamp; and
an integrated circuit (IC) chip connected intermediate the power
source and the lamp, the IC chip containing switching means
connected to the power source and the lamp for delivering power to
the lamp, a drive means connected to said switching means for
operating said switching means, an oscillator means connected to
said drive means for operating said drive means at a certain
frequency, and a control means connected to said oscillator means
for setting said oscillator means at said frequency.
6. The system of claim 5 further comprising,
a current limiting circuit connected intermediate the lamp and the
IC chip.
7. The system of claim 5 further comprising,
a second fluorescent lamp connected to said switching means of the
IC chip and wherein said control means operating said switching
means to alternately supply power to said first and second lamps at
said frequency.
8. The system of claim 5 wherein,
the IC chip further comprises a rectifier connected intermediate
the power source and said switching means.
9. The system of claim 5 further comprising,
a variable voltage means connected intermediate the power source
and said switching means of the IC chip for varying a voltage from
the power source; and
the IC chip further comprising a voltage compensator means
connected to the variable voltage means and said control means, for
sending a signal to said control means to change said frequency
responsive to a change in said voltage.
10. The system of claim 5 wherein,
the IC chip further comprises a load status detection means
connected to said switching means and said control means for
monitoring a power level in said switching means and providing a
shut off signal to said control means when said power level exceeds
a certain value.
11. The system of claim 5 wherein,
the IC chip further comprises a thermal overload means connected to
said drive means, for measuring a temperature level inside the IC
chip and providing a shut down signal to said drive means when said
temperature level exceeds a certain value.
12. The system of claim 5 wherein,
said frequency is between twenty-five and fifty kilohertz.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to fluorescent lamp systems and
more particularly to such systems wherein the lamp is operated at a
high frequency by means of control logic and power switching
devices which are located on a single integrated circuit chip.
2. Description of the Prior Art
Fluorescent lamps require a ballast circuit because fluorescent
lamps have a negative resistant characteristic. As current flowing
through the lamp increases, voltage across the lamp decreases.
Eventually, the lamp will act like a short circuit if the current
is not limited in some way.
A ballast circuit acts to limit current flowing through the lamp.
The typical ballast circuit operates at line frequency (sixty
hertz) and is primarily just a large inductor. This simple type of
ballast circuit has been used with fluorescent lamps for many
years. It does however have some disadvantages. The large inductor
makes the circuit heavy and bulky. It is also inefficient because
fluorescent lamps operate at optimum efficiency at higher
frequencies in the range of twenty-five kilohertz to fifty
kilohertz.
Prior art systems have been made which operate fluorescent lamps in
this higher frequency range. However, the complexity of these
systems has made them highly unreliable and costly compared with
the simple inductor ballast systems. Even though the lamp operates
more efficiently, the energy savings has not been enough to off-set
the initial high cost of these lamp systems and thus, they have not
been economically viable. Examples of such systems include U.S.
Pat. No. 4,170,746, issued to J. Davenport; U.S. Pat. No.
4,544,862, issued to H. Yamazaki, et al.; U.S. Pat. No. 4,220,895,
issued to E. Nuver; and U.S. Pat. No. 4,306,177, issued to I.
Kaneda.
Various federal and state codes have been passed recently which
call for more efficient lighting. There is a need for an efficient
and low cost fluorescent lamp system.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide a
fluorescent lamp system which is efficient, reliable and
inexpensive.
It is another object of the present invention to provide a
fluorescent lamp system which achieves high frequency power
switching on a single integrated circuit chip.
Briefly, in a preferred embodiment, the present invention comprises
a "Smart Power" integrated circuit (IC) chip, an AC power source,
and a fluorescent lamp. The IC chip has a voltage regulator to
provide power to various logic circuits on the chip. The power
source is connected to the lamp through power transistors located
on the IC. A control and diagnostic circuit is connected to and
sets the frequency for a frequency oscillator and charge pump
circuit. The frequency oscillator and charge pump circuit is
connected to and provides a timing signal to a drive circuit. The
drive circuit is connected to and controls the power transistors
such that the lamp is driven at the desired frequency. A thermal
overload circuit is connected to the drive circuit to provide a
thermal shut down signal if the IC gets too hot. A load status
detection circuit is connected between the lamp and the control and
diagnostic circuits and provides a shut off signal to protect
against overload. A voltage compensation circuit is connected to
the power source and the controlling diagnostic circuit and allows
for an optional dimming feature.
An advantage of the present invention is that it provides a
fluorescent lamp system which is efficient, reliable and
inexpensive.
It is another advantage of the present invention in that it
provides a fluorescent lamp system which achieves high frequency
power switching on a single integrated circuit chip.
These and other objects and advantages of the present invention
will no doubt become obvious to those of ordinary skill in the art
after having read the following detailed description of the
preferred embodiments which are illustrated in the various drawing
figures.
IN THE DRAWINGS
FIG. 1 shows a schematic of a first embodiment of the system of the
present invention;
FIG. 2 shows a schematic of an integrated circuit chip of FIG.
1;
FIG. 3 shows two graphs illustrating the amount of current flowing
through the lamps of FIG. 1;
FIG. 4 shows a schematic of a second embodiment of the system of
the present invention;
FIG. 5 shows a graph illustrating the amount of current flowing
through the lamp of FIG. 4; and
FIG. 6 shows a schematic of a third embodiment of the system of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a schematic of a first embodiment of a fluorescent
lamp system of the present invention and is designated by the
general reference number 10. An alternating current power source 12
is connected to an integrated circuit (IC) 14. The power source 12
is typically a standard line source (one hundred twenty volts AC,
sixty hertz).
The IC 14 has a plurality of output terminals 16, 17, 18 and 19.
Output terminal 16 is connected to a resistor 22 which in turn is
connected to a terminal 24 of a fluorescent lamp 26. A capacitor 28
is connected to terminal 17 and a terminal 30 of lamp 26. A
capacitor 32 is connected intermediate terminal 30 and a terminal
34 of lamp 26. A terminal 36 of lamp 26 is connected to ground.
A resistor 40 is connected between terminal 18 and a terminal 42 of
a fluorescent lamp 44. A capacitor 46 is connected between terminal
19 and a terminal 48 of lamp 44. A capacitor 50 is connected
between terminal 48 and a terminal 52 of lamp 44. A terminal 54 of
lamp 44 is connected to ground. Resistors 22 and 40 and capacitors
28, 32, 46 and 50 limit the current flowing through lamps 26 and
44.
FIG. 2 shows a schematic of IC 14 of FIG. 1. The IC 14 has a pair
of input terminals 60 and 62 which are connected to power source
12. A voltage regulator circuit 64 is connected to terminal 60.
Circuit 64 is connected to and provides power to a control and
diagnostic circuit 66. A high frequency oscillator and charge pump
circuit 68 is connected to the control and diagnostic circuit 66.
Circuit 68 has a variable speed oscillator which can be set to run
at frequencies between twenty-five kilohertz and fifty kilohertz
responsive to control circuit 66.
A drive, load clamp, and current limiting circuit 70 is connected
to circuit 68. Circuit 70 is connected to a plurality of power
transistors 72, 74, 76, 78, 80, 82, 84 and 86. Transistors 72, 76,
80 and 84 are each connected between terminal 60 and terminals 16,
17, 18 and 19, respectively. Transistors 74, 78, 82 and 86 are each
connected between terminal 62 and terminal 16, 17, 18 and 19,
respectively.
A thermal overload shut down circuit 100 is connected to the drive
circuit 70. A load status detection circuit 102 is connected
between terminals 16, 17, 18 and 19 and the control circuit 66. A
voltage compensation circuit 104 is connected between terminal 60
and control circuit 66. Circuits 64, 66, 68, 70, 100, 102 and 104
comprise a control and drive (CD) section 110 of IC 14.
The IC 14 is made by using the process for manufacturing "Smart
Power" IC chips. "Smart Power" is a trademark of the SGS Company of
Italy. Micrel Company of Sunnyvale, Calif., is also involved in the
manufacture of chips using this process. This process allows for
the manufacture of single IC chips which contain both logic
circuits and power switching devices.
In operation, the power source 12 provides an alternating current
across terminals 60 and 62. The voltage regulator circuit 64
supplies power to the logic circuits of the control circuit 66. The
control circuit 66 sets the high frequency oscillator circuit 68 to
run at a certain frequency, such as twenty-five kilohertz. The high
frequency oscillator and charge pump circuit 68 provides
twenty-five kilohertz timing pulses to the drive circuit 70.
Circuit 70 has load clamp and current limiting devices to protect
the circuitry from any overloads. The drive circuit 70 uses the
timing pulses from circuit 68 to provide control pulses to
transistors 72, 74, 76, 78, 80, 82, 84 and 86. These transistors
are operated such that the alternating current from terminals 60
and 62 is alternately switched between lamps 26 and 44 at a high
frequency, such as twenty-five kilohertz. For example, when
transistors 72 and 76 allow current to flow to lamp 26, transistors
80 and 84 are controlled to block the flow of current to lamp 44.
Thus, the present invention is able to use a standard sixty hertz
alternating current line and drive the lamps at the more efficient
higher frequency.
FIG. 3 shows a pair of graphs 120 and 122 which represent the
current flows through lamps 26 and 44, respectively. Graphs 120 and
122 represent the standard sixty hertz alternating current sine
wave which has been chopped up at the frequency rate of the
oscillator circuit 68. During the time period when graph 120 shows
a current flow, graph 122 shows a zero current flow and vice
versa.
Returning now to FIG. 2, as the system 10 operates, the thermal
overload shut down circuit 100 constantly monitors the temperature
of IC 14. If the temperature goes over an acceptable limit, circuit
100 sends a thermal shut down signal to drive circuit 70 which
causes drive circuit 70 to shut down. Circuit 70 causes the
transistors 72-86 to block the flow of current to lamps 26 and
44.
The load status detection circuit 102 measures the power flowing to
lamps 26 and 44. If a short circuit is detected, circuit 102 sends
a shut-off signal to the control circuit 66. Circuit 66 then causes
oscillator 68 to shut off and this in turn blocks the flow of power
to lamps 26 and 44.
The voltage compensation circuit 104 provides for an optional
dimming feature. A dimming device or switch 112 may be connected
between power source 12 and IC 14. This device 112 is used to dim
standard incandescent lamps by varying the voltage to the lamps.
Ordinarily, these dimmers are not used with fluorescent lamps
because as the voltage across the lamp is reduced, the filament
voltage is also reduced. This causes the fluorescent lamp to go
out.
Voltage compensator circuit 104 detects when the voltage drops as a
result of the dimmer 112. The circuit 104 compensates for the
reduced voltage by sending a signal to control circuit 66 which
causes circuit 66 to run the oscillator 68 at a higher frequency.
The higher frequency compensates for the reduced filament voltage
and allows lamps 26 and 44 to remain lit at a reduced voltage and
consequently a reduced light intensity.
FIG. 4 shows an alternative embodiment of the system of the present
invention and is designated by the general reference number 200.
Elements of system 200 which are similar to elements of system 10
of FIGS. 1 and 2 are designated by a prime number. An IC 202 is
connected to an alternating current power source 12' at a pair of
terminals 204 and 206. IC 202 is manufactured using processes for
the "smart power" chip. A control and drive section 110' is
connected to and controls a plurality of bi-directional switches
210, 211, 212 and 213 on IC chip 202. Switch 210 is connected
between terminal 204 and a terminal 220. Switch 211 is connected
between terminal 204 and a terminal 222. Switch 212 is connected
between terminal 206 and terminal 220. Switch 213 is connected
between terminal 206 and terminal 222.
A transformer 224 has a first winding 226, a second winding 228,
and a third winding 230. First winding 226 of transformer 224 and a
capacitor 232 are connected in series across terminals 220 and 222.
An inductor 234 is connected to terminal 222. A fluorescent lamp
240 has a plurality of terminals 242, 244, 246 and 248. Terminal
244 is connected to inductor 234 and second winding 228. Terminal
242 is connected to second winding 228. Terminal 246 is connected
to third winding 230. Terminal 248 is connected to third winding
230 and terminal 220.
During operation of system 200, the control and drive section 110'
operates similar to section 110 of system 10. A drive, load clamp
and current limiting circuit in section 110' controls switches
210-213. Switches 210 and 213 are open when switches 211 and 212
are closed, and visa versa. The switches 210-213 are operated at a
high frequency, such as twenty-five kilohertz. The result is that
lamp 240 is driven at a high frequency. Transformer 224, capacitor
232 and inductor 234, form a current limiting circuit 260.
FIG. 5 shows a graph 300 of the current flowing to lamp 240 of
system 200. The graph 300 shows a standard sixty hertz sine wave
which is alternately inverted at a high frequency.
FIG. 6 shows another alternative embodiment of the system of the
present invention and is designated by the general reference number
400. Elements of system 400 which are similar to elements of system
10 of FIGS. 1 and 2 are designated by a double prime number.
An IC chip 402 is connected to an alternating current power source
12" at a pair of terminals 404 and 406. IC chip 402 is manufactured
using processes for a "smart power" chip. IC 402 contains a full
wave rectifier 410 which is comprised of a plurality of diodes 412,
414, 416 and 418. Rectifier 410 is connected to terminals 404 and
406 and has a pair of output terminals 420 and 422.
A control and drive section 110" is connected to terminals 404 and
406. Section 110" is connected to and controls a plurality of DMOS
field effect transistors 430, 432, 434 and 436. IC 402 has a pair
of output terminals 440 and 442. Transistor 430 is connected
between terminals 420 an 442. Transistor 432 is connected between
terminals 420 and 440. Transistor 434 is connected between
terminals 422 and 442. Transistor 436 is connected between
terminals 422 and 440.
A transformer 444 has a first winding 446, a second winding 448 and
a third winding 450. First winding 446 of transformer 444 and a
capacitor 452 are connected in series across terminals 440 and 442.
An inductor 454 is connected to terminal 140. A fluorescent lamp
260 has a plurality of terminals 462, 464, 466 and 468. Terminal
462 is connected to second winding 448. Terminal 464 is connected
to inductor 454 and second winding 448. Terminal 466 is connected
to third winding 450. Terminal 468 is connected to third winding
450 and terminal 442.
During operation of system 400, the rectifier 410 rectifies the
incoming alternating current from terminals 404 and 406 and
produces a fully rectified current at terminal 420 and 422. The CD
110" operates similar to section 110 of system 10. A drive, load
clamp and current limiting circuit in section 110" controls
transistors 430-436. Current is allowed to flow through transistors
430 and 436 while current is being blocked from flowing through
transistors 432 and 434 and vice versa. The transistors are
operated in alternate fashion at a high frequency, such as
twenty-five kilohertz. The flow of current through lamp 260 is
similar to that depicted in graph 300 of FIG. 5. The rectified
sixty hertz sine wave is alternately inverted at the set high
frequency. Transformer 444, capacitor 452, and inductor 454 form a
current limiting circuit 470.
The present invention provides many benefits over prior art
systems. The present invention utilizes a high frequency design
which operates the fluorescent lamp at optimum efficiency. The
present invention is realized by a unique IC chip which contains
both logic and power switches. This greatly reduces the cost and
enhances the reliability of the system.
Although the present invention has been described in terms of the
presently preferred embodiments, it is to be understood that such
disclosure is not to be interpreted as limiting. Various
alterations and modifications will no doubt become apparent to
those skilled in the art after having read the above disclosure.
Accordingly, it is intended that the appended claims be interpreted
as covering all alterations and modifications as fall within the
true spirit and scope of the invention.
* * * * *